What are the recycling process and introduction of PVC plastic?
所属分类:Recycling and utiliz
The new technologies that are now being developed include the solvent method, mechanical method, and chemical method, among which the solvent method is a newly developed technology in Europe.4....

       The new technologies that are now being developed include the solvent method, mechanical method, and chemical method, among which the solvent method is a newly developed technology in Europe.

4.1 Solvent method

4.1.1 Vinyloop Process

        This process was developed by Solvay SA and several of its industrial partners and was named the Vinyloop process. This process is used to recover copper-containing and rubber-containing cable materials after copper removal, and operates in a batch process. For recycling, the raw material is first separated by an electrostatic separator to obtain a PVC/rubber material, which is ground and sent to a dissolver. The solution is dissolved in methyl ethyl ketone (MEK) and the resulting solution is sent to the spin filter. The device removes undissolved impurities and other contaminants by special filtration. The filtrate was sent to a precipitator, additives were added to the solution, and steam was blown to precipitate PVC as small pellets. The solvent is then evaporated, condensed, and sent to the dissolver for recycling. The obtained PVC pellets enter the spin dryer predryer, and then enter the air dryer to dry and become a PVC with good dispersion. Its density is similar to the new PVC, but the material is usually gray, because PVC contains The pigments and various additives are difficult to remove. However, because the temperature of each step of this process is not higher than 115cc, the performance of PVC is basically not deteriorated. The Vinyloopl process is economically viable because recycled PVC pellets can be used directly without further granulation.

        In principle, the Vinyloop process is used to treat a variety of PVC wastes and materials, such as cable coatings and insulation, floors, etc. The recovered PVC can still be used as raw materials. However, it is not possible to mix the cable material with the crushed floor material because various lead stabilizers in the PVC cable material are compatible with each other, and various tin stabilizers in the PVC flooring are also compatible, but lead stabilizers and tin After the stabilizers are mixed, the recycled PVC is brown.

4.1.2 Delphi Process

        The second new process to recycle PVC by solvent is used to recover PVC from the entire automotive panel.

        The process was jointly developed by the DelPhl Automotive Plant in Wuppertal, Germany, and WuDDertal University. Three years ago, it was industrialized by Wietek Gmbh, an automotive recycling company in Nohfe Iden-Eisen, Germany. Using this process to recycle PVC costs less than 20% of the new PVC price. The process uses esters and ketones as solvents, but the amount of solvent is much less than the Vinyloop process. In the Delphi process, the solvent does not completely dissolve the waste PVC, but only softens it, making it easy to separate from the copper wire, and the resulting copper wire can be used to pay for the recycling process. Wietek has invented a process for separating plastics and solvents using centrifugation and has obtained patent rights. Because when the cable with PVC jacket or insulation layer is recovered by this process, the cable is not cut off, so the recycling process is dust-free and there is no need to filter and separate the metal. Wietek's recycling PVC production line established according to this process can recover 255 tons of reusable PVC each year, and the production line can also be used to recover certain other materials. For example, Wietek has successfully developed a solvent method. Automotive grilles and luminaires, and certain metal-containing plastic parts, are a new process for recycling ABS (Acrylonitrile Butadiene Styrene Copolymer) and ABS plant acrylic resins.

4.2 Mechanical method

        The use of mechanical methods can recover a variety of PVC products, including pipes, cable materials, plates, films, automotive components and bottles. PVC recycled after this method can be reused in the manufacture of many products, including window frames, floor mats, floors, protective panels, acoustic panels, pipe fittings, drains, coatings, non-food bottles, etc., and can even be used to make fibers. And secondary computer components. For the recycling of PVC bottles, the mechanical method has been industrialized. The following mainly introduces the Solvayl process.

        Solvayl Process - When using the Solvayl process, bundled PVC bottles are first loosened on a bulkhead debonder, such as a PET bottle, using an XR F (X-ray fluorescence) automated system or manually operated UV ( Ultraviolet (UV) systems separate PET bottles from PVC bottles (recycled bottles are usually mixed with PVC bottles and PET bottles). The bottle is then passed through a metal detector to remove any metal debris from the bottle stream to prevent it from damaging the crushing equipment downstream of the process. Subsequently, just after C is crushed into sheets, the latter is fed into a set of centrifugal separators using an auger, where they remove soft materials such as paper labels, plastic films, and dirt adhering to bottles. , and PVC caps on the aluminum sheet can be removed using an electrostatic separator. In the crushing process, the size of the formed PVC sheet is a critical factor, and the sheets should not be too small, otherwise they will be removed together with the soft paper labels, plastic films and the like. In addition, the size of the PVC sheet should be larger than the diameter of the centrifugal filter screen, otherwise it will clog the screen and reduce the screening efficiency. The centrifugally separated PVC sheet is then conveyed into a floatation separation tank using an auger. In this tank, impurities such as polyolefin and styrofoam in the P VC sheet float, while the PVC and PET sheets are When they sink, they are separated. The sheet obtained by the above treatment is recovered and dried, wherein the content of PVC is greater than 99%. This PVC can be further purified by melt filtration so that the P E T content therein is less than 100 μg/L. This pure PVC can be used for granulation and processing into products.

        The PVC sheet and P E T sheet can also be separated by fine sieving and then sieving. Because the PVC and PET have different brittleness, the PVC and P E T sheets obtained after the comminution are different in size, so the two can be separated by sieving. However, the PET bottle neck and the bottom material behave similar to PVC in the crushing process, so this part of the material is also mixed in the PVC and cannot be separated. It can also use foam flotation or electrostatic separation of PVC and PET.

4.3 Chemical method

         PVC detritus can be oxidized to oxalic acid and benzoic acid in oxygenated sodium hydroxide solution at 150-260 degrees Celsius and under high pressure. Under optimal conditions, It PVC produces 600 kg oxalic acid and 300 kg benzoic acid. When the concentration of sodium hydroxide in the hydroxide solution wKiAiVFuFYmkmzWEAABoXXMe_2Y434.jpg is lower than 15 m ol/L, the solution concentration is increased and the oxalic acid production is increased. The figure on the right shows the oxidation reaction of PVC. The first step of the reaction (a) is the removal of HC I from PVC to produce multiolefins, and the second step (b) is the formation of aromatic rings by the addition of a bimolecular addition reaction and the cyclization of polyenes under the action of oxygen. ) is the liquid phase oxidation of aromatic compounds to produce benzoic acid. Through the alkali-catalyzed oxidation of liquid phase, all three olefins, aromatic compounds and benzoic acid can be converted into oxalic acid and C02. At a partial pressure of 2500C and 5 MPa oxygen, PVC detritus can be completely decomposed in a concentration of 15 mOl/L sodium hydroxide solution within 12 h. This method can be used to recycle PVC or soft PVC containing fillers because plasticizers (such as phthalic acid esters) in soft PVC can also be oxidized to oxalic acid.

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